Replacing Turret Board Components

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mkel2010
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Replacing Turret Board Components

Post by mkel2010 »

In order to try to reduce the amount of hiss coming from my amp (build thread here: viewtopic.php?f=4&t=25860) I need to replace some carbon film resistors with metal film. When I built the turret board, I installed the component leads into the turret holes and then soldered them in (whether right or wrong, it's done.) Is it acceptable to clip the existing leads to remove the resistors and then install the new leads by making a mechanical connection to the outside of the turret and solder there? My previous attempts at desoldering components on circuit boards yielded less than stellar results so I'm looking for the best way to replace the parts without doing a bunch of desoldering or buying a vacuum desoldering station.

In my build thread, it was also suggested that I change the cathode bypass cap to a larger one. I've purchased several different sizes and am wondering if there is a way to temporarily bypass the existing cathode bypass cap to see how the amp sounds with a different one before committing to the change?
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Re: Replacing Turret Board Components

Post by JMPGuitars »

You could clip the leads, and make j-hooks to connect new components. But that's not ideal.

I have an Aoyue 2703A+ station that has the vacuum desoldering gun, it's wonderful, and reasonably priced.

For the capacitor, it doesn't matter. You can install them in parallel. Parallel capacitance is the sum of the parallel capacitors. In parallel a 50uF plus 100uF cap = 150uF.

Thanks,
Josh
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Re: Replacing Turret Board Components

Post by mkel2010 »

JMPGuitars wrote:
Wed 04/21/21 2:38 pm

I have an Aoyue 2703A+ station that has the vacuum desoldering gun, it's wonderful, and reasonably priced.

For the capacitor, it doesn't matter. You can install them in parallel. Parallel capacitance is the sum of the parallel capacitors. In parallel a 50uF plus 100uF cap = 150uF.
Thank you, Josh. I went ahead and ordered a vacuum desoldering station, the Aoyue 474++, since yours would be a little overkill for my purposes.

With regards to the parallel capacitors, could I temporarily make the connection with alligator clips to see how one sounds or would that not work?

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Re: Replacing Turret Board Components

Post by JMPGuitars »

mkel2010 wrote:
Wed 04/21/21 4:38 pm
With regards to the parallel capacitors, could I temporarily make the connection with alligator clips to see how one sounds or would that not work?
The issue with alligator clips is the question of the quality of the connection, and the possibility of shorting something out if they slip.

The best way to test temporarily, is to just use a drop of solder on the leads. You can solder permanently when you decide the value you like.
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Re: Replacing Turret Board Components

Post by zaphod_phil »

JMPGuitars wrote:
Wed 04/21/21 2:38 pm
I have an Aoyue 2703A+ station that has the vacuum desoldering gun, it's wonderful, and reasonably priced.

\
And you can desolder a vacuum with that thing? Wow!! 8O :lol:
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Re: Replacing Turret Board Components

Post by zaphod_phil »

mkel2010 wrote:
Wed 04/21/21 12:08 pm
In order to try to reduce the amount of hiss coming from my amp (build thread here: viewtopic.php?f=4&t=25860) I need to replace some carbon film resistors with metal film. When I built the turret board, I installed the component leads into the turret holes and then soldered them in (whether right or wrong, it's done.) Is it acceptable to clip the existing leads to remove the resistors and then install the new leads by making a mechanical connection to the outside of the turret and solder there? My previous attempts at desoldering components on circuit boards yielded less than stellar results so I'm looking for the best way to replace the parts without doing a bunch of desoldering or buying a vacuum desoldering station.

In my build thread, it was also suggested that I change the cathode bypass cap to a larger one. I've purchased several different sizes and am wondering if there is a way to temporarily bypass the existing cathode bypass cap to see how the amp sounds with a different one before committing to the change?
Most of your hiss will be from preamp tubes.You may need to try lower noise types. Carbon film resistors aren't generally very noisy - carbon comp resistors are :evil: . Not sure how a different cathode cap is supposed to help with the hiss problem :roll:
Also note that ultrasonic oscillations can also sound to our ears like a hiss. So maybe start by chopsticking leads and making sure to use shielded wire for longer signal connections.
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Re: Replacing Turret Board Components

Post by JMPGuitars »

zaphod_phil wrote:
Sat 05/01/21 6:32 pm
And you can desolder a vacuum with that thing? Wow!! 8O :lol:
If it will fit on the bench sure, but working on one would really suck. 😲
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Re: Replacing Turret Board Components

Post by TriodeLuvr »

Vacuum stations for turret boards?? It's totally unnecessary to spend that kind of money for this work.

Image

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Re: Replacing Turret Board Components

Post by JMPGuitars »

TriodeLuvr wrote:
Sat 05/01/21 10:12 pm
Vacuum stations for turret boards?? It's totally unnecessary to spend that kind of money for this work.

Jack
$300 for a complete rework station with hot air, soldering, and desoldering is a darn good price. I don't like those manual pumps, too much effort, and never great results. I wouldn't suggest somebody pay $300 just for the desoldering gun, but I guess some people would still consider that cheap.
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Re: Replacing Turret Board Components

Post by zaphod_phil »

JMPGuitars wrote:
Sat 05/01/21 7:42 pm
zaphod_phil wrote:
Sat 05/01/21 6:32 pm
And you can desolder a vacuum with that thing? Wow!! 8O :lol:
If it will fit on the bench sure, but working on one would really suck. 😲
:lol: :lol: :lol:
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Re: Replacing Turret Board Components

Post by mkel2010 »

I have replaced the carbon comp resistors at the inputs and the plate resistors at V1 and V2 with metal film. The hiss is greatly reduced, but still overwhelms the guitar when the gain and volume are beyond about 60 to 70%. I have six different 12AX7 tubes that I've swapped around and it does not seem to have any effect on the hiss at the higher gain and volume levels. I have chop-sticked several times and found a loose wire that was causing a different problem and is now fixed. I did use shielded wire for the inputs and TMB channel's gain wiring. The amp is usable now, but I may look at replacing some of the other carbon comp resistors in the signal chain down the road.

The vacuum desoldering system that I got (Auyoe 474A++, $145 on Amazon) was very useful and allowed me to do the desoldering with one hand and have the other hand free. I have a manual pump but found that much more awkward to use. The cost of the unit was worth it to me.
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Re: Replacing Turret Board Components

Post by JMPGuitars »

mkel2010 wrote:
Tue 05/04/21 6:46 pm
I have replaced the carbon comp resistors at the inputs and the plate resistors at V1 and V2 with metal film. The hiss is greatly reduced, but still overwhelms the guitar when the gain and volume are beyond about 60 to 70%. I have six different 12AX7 tubes that I've swapped around and it does not seem to have any effect on the hiss at the higher gain and volume levels. I have chop-sticked several times and found a loose wire that was causing a different problem and is now fixed. I did use shielded wire for the inputs and TMB channel's gain wiring. The amp is usable now, but I may look at replacing some of the other carbon comp resistors in the signal chain down the road.

The vacuum desoldering system that I got (Auyoe 474A++, $145 on Amazon) was very useful and allowed me to do the desoldering with one hand and have the other hand free. I have a manual pump but found that much more awkward to use. The cost of the unit was worth it to me.
I agree completely, the Aoyue desoldering stuff is great.

Have you made any changes to your grounding scheme yet? Check my previous messages if you have not.
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Re: Replacing Turret Board Components

Post by mkel2010 »

JMPGuitars wrote:
Tue 05/04/21 7:52 pm

Have you made any changes to your grounding scheme yet? Check my previous messages if you have not.
Josh,

The grounding scheme used on my amp is exactly as you describe in your signature link.

There are three ground points: The IEC has it's own ground; a separate power ground and a separate preamp/input/controls ground.

I'm not sure what you would have me change?

For reference, here are the layout and schematic drawings:
18WattSIIILayout6.pdf
18WattSIIISchematic13.pdf
Mark
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Re: Replacing Turret Board Components

Post by JMPGuitars »

mkel2010 wrote:
Wed 05/05/21 3:47 pm
Josh,

The grounding scheme used on my amp is exactly as you describe in your signature link.

There are three ground points: The IEC has it's own ground; a separate power ground and a separate preamp/input/controls ground.

I'm not sure what you would have me change?

For reference, here are the layout and schematic drawings:

18WattSIIILayout6.pdf
18WattSIIISchematic13.pdf

Mark
That's a good start, but it's not the same. Read the thread again and review the layout to see how the preamp grounds are actually run.

Thanks,
Josh
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Re: Replacing Turret Board Components

Post by mkel2010 »

JMPGuitars wrote:
Wed 05/05/21 5:02 pm

That's a good start, but it's not the same. Read the thread again and review the layout to see how the preamp grounds are actually run.

Thanks,
Josh
OK. I think I see the difference: You're position is that the preamp bus ground is attached at the input jack instead of the chassis ground point shared with the input jack in my layout, correct?

Can you help me understand how the two grounding schemes are different and why one is better than the other (trying to learn is the reason for the question?) I've tried to find explanations that are understandable but haven't had a great deal of success.

If I change the ground bus to the input jack, does it matter to the effectiveness of the ground connection which of the input jack ground lugs is used?
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